High tensile steel having high notch toughness

ABSTRACT

A HIGH TENSILE STEEL COMPRISING 0.12-0.21% OF CARBON, 0.70-1.00% OF MANGANESE, 0.20-0.35% OF SILICON, 0.400.65% OF CHROMIUM, 0.15-0.25% OF MOLYBENUM, 0.030.08% OF VANADIUM 0.01-0.03% OF TITANIUM, 0.00050.0005% OF BORON, 0.020-0.60% OF ALUMINUM, 0.0080.020% OF NITROGEN AND THE BALANCE BEING IRON AND IMPURITIES, TREATED BY HARDENING AND TEMPERING TO PROVIDE THE STEEL WITH A YIELD POINT OF MORE THAN 70 KG./MM.2. A TENSILE STRENGTH OF MORE THAN 80 KG./MM.2. AND AN EXCELLENT NOTCH TOUGHNESS AND WELDABILITY.

United States Patent 3,664,830 HIGH TENSILE STEEL HAVING HIGH N OTCH TOUGHNESS Akira Kambayashi and Shun-ichi Shimada, Kawasaki, and Takashi Ehara, Tokyo, Japan, assignors to Nippon Kokan Kabushiki Kaisha, Kawasaki-shi, Japan No Drawing. Filed June 15, 1970, Ser. No. 46,475 Claims priority, application Japan, June 21, 1969, Vi/48,794 Int. Cl. C22c 37/10, 39/14 US. Cl. 75-124 2 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a high tensile steel.

SUMMARY OF THE INVENTION The steel of the invention comprises 0.12-0.21% of carbon, 0.70l.00% of manganese, 0.20-0.35% of silicon, 0.400.65% of chromium, 0.l50.25% of molybdenum, 0.030.08% of vanadium, 0.01-0.03% of titanium, 0.00050.005% of boron, 0.020-0.060% of aluminum, ODDS-0.020% of nitrogen and the balance being iron and impurities. It is treated by hardening and tempering to provide a steel with a yield point of more than 70 kg./mrn. a tensile strength of more than 80 kg./mm. and an excellent notch toughness and weldability.

BACKGROUND OF THE INVENTION ASTM A 517 GrB, USS T-1 Type A Steel is known in the art as a steel of this type. However, when such a high tensile strength steel was compared with steel containing nickel and having an equal high tensile strength, it was found to be lacking in notch toughness. Thus, such a known steel is not suitable as a high tensile strength steel for severe conditions of use.

The present invention provides a steel which has both the high tensile strength and the notch toughness of the known steel containing expensive nickel, but at a lower cost and on an industrial scale. The steel, after nitrogen and aluminum addition, is hardened and tempered to precipitate nitrided aluminum.

DESCRIPTION OF SPECIFIC EMBODIMENTS The upper limit of the aluminum content is set at 0.060%. This is because more than 0.060% of aluminum is likely to harm the purity of steel. The upper limit of the content of nitrogen is set at 0.020% to fix the same with respect to the above-mentioned upper limit of the aluminum content. The lower limit of the aluminum content is set at 0.020%. This is because less than 0.020% of aluminum cannot be expected to achieve deoxidation of the steel and complete fixation of solidified nitrogen. The lower limit of the nitrogen content is set at 0.008% bearing in mind the relationship between the amount of added aluminum and the required amount of nitrided aluminum.

3,664,830 Patented May 23, 1972 EXAMPLE Table 1 shows an example of the chemical composition of a steel of the present invention, the balance being iron and impurities, Table 2 shows the mechanical properties of a steel obtained by rolling the steel shown in Table 1 into a plate of gauge 25 mm. and by a heat-treatment comprising hardening and tempering.

TABLE 1 Percent C 0.17 Si 0.26

Mn 0.93 P 0.015 S 0.007 Cr 0.63 Mo 0.24 V 0.04 Ti 0.01 B 0.002 A1 0.040 N 0.012

TABLE 2 Tensile test Impact test Plato Tensile vEO vE-GO gauge Yield point strength Elongation (kgmJ (kgmJ vTs (mm.) (kg/mm?) (kg/nun!) (percent) cmfl) em?) C.)

Notes to Table 2 The materials subjected to the tensile test had a gauge length (G.L.) of two inches and a diameter of 14 mm.

The materials subjected to the impact test contained a. 2 mm. V-shaped notch.

From a study of the above example, it can be established that the steel of this invention is superior to known high tensile steels both in yield point and tensile strength. In addition, it possesses a high notch toughness even at a temperature of 60 C. Consequently, the steel of this invention is comparable to known expensive high tensile steel containing nickel and is very useful for low-temperature service as a high tensile steel.

We claim:

1. A high tensile steel comprising 0.l2-0.21% of carbon, 0.701.00% of manganese, 0.20-0.35% of silicon, 0.400.65% of chromium, 0.15-0.25 of molybdenum, 0.030.08% of vanadium, 0.01-0.03% of titanium, 0.00050.005% of boron, 0.020-0.060% of aluminum, 0.008-0.020% of nitrogen and the balance being iron and impurities, and treated by hardening and tempering.

2. A high tensile steel comprising 0.17% carbon, 0.93% manganese, 0.26% silicon, 0.63% chromium, 0.24% molybdenum, 0.04% vanadium, 0.01% titanium, 0.002% boron, 0.040% aluminum, 0.012% nitrogen, the balance being iron and impurities.

References Cited UNITED STATES PATENTS 2,858,206 10/1958 Boyce -126 D 3,291,655 12/1966 Gill 75--126 D 3,310,441 3/1967 Mandich 75124 HYLAN D BIZOT, Primary Examiner US. Cl. X.R.

75126 C, 126 D, 126 I, 126 J 

